1. Field of the Invention
The present invention relates to an expanded polystyrene-based resin formed product comprising a rubber-like latex and melamine cyanurate, and relates to a production method thereof.
2. Description of the Related Art
An expanded polystyrene-based resin formed product has excellent heat resistance and cushioning property due to the presence of closed cells. However, it has defects that the surface of a formed product is brittle, mechanical strength is low, etc., because of the low density (light weight) thereof. In addition, it has defects that, due to combustibility of a polystyrene base material, and due to air in cells and a remaining combustible expanding agent, an expanded styrene resin-based formed product is easily burned when placed near an ignition source. Further, in a styrene-based resin formed product, static electricity tends to be generated easily and hence dust is easily adhered thereto. In addition, when formed products are rubbed, unpleasant squeak noises are generated. Under such circumstances, elimination of these defects to increase its demand has been desired.
As attempts to overcome these defects, the inventors of the present invention proposed expandable styrene-based resin particles having a rubber-like latex on the surfaces thereof (Patent Document 1). However, although hardness or mechanical strength of the surface of a formed product is improved, effects of flame retardancy have not yet been obtained. Further, the inventors of the present invention proposed to incorporate an inorganic compound by utilizing a binder function of a rubber-Like latex (Patent Document 2). However, although combustibility is lowered, effects of attaining high expandability have not yet been realized.
As known methods for imparting flame retardancy that has heretofore been conducted include: a method in which expandable polystyrene resin particles during the process of synthesis are impregnated with a bromine- or chlorine-containing organic halogen compound singly or in a mixture with an organic peroxide; a method in which a styrene-based resin is kneaded together with a bromine- or chlorine-containing organic halogen compound by means of an extruder, followed by forming a sheet or a board with an expanding agent added (Patent Document 3); etc. However, in these methods, a toxic halogen compound is generated as a combustion gas, and may cause health damage or environmental contamination. Further, due to the presence of a halogen compound in these formed products, recycling is difficult. In order to burn them as an industrial waste, not only a special incinerator that enables high-temperature combustion is required but also expensive capital investment and a huge amount of running cost are incurred.
Further, other proposed method include: a method in which brominated polystyrene is used (e.g. Patent Document 4); a method in which a brominated diphenyl compound and an antimony oxide are mixed (e.g. Patent Document 5); and a method in which an organic phosphorus-based additive is incorporated as a flame retardant (e.g. Patent Documents 6 and 7) are proposed. Each of these materials is not only expensive but also may lead to health damage or environmental contamination.
For preventing generation of static electricity, generally known technology is a method in which a formed product is impregnated with a surfactant of which the hydrophilic group contains an anion or a cation, a nonionic surfactant or the like or a method in which such a surfactant is applied to a formed product. However, in this method, a surfactant is peeled off readily from the surface of a formed product, and hence, effects of continuously suppressing generation of static electricity are insufficient.
In order to prevent generation of squeak noises that are generated when expanded polystyrene-based resin formed products are rubbed, with an aim of improving slidability of a formed product, conducted is a method using, as a lubricant, soap such as metal salts of a higher fatty acid. Specifically, a method in which expandable polystyrene resin particles are impregnated with such soap or a method in which such soap is adhered to the surface of an expanded polystyrene resin formed product is adopted. However, advantageous effects of the methods are not sufficient. Further, a method in which an unwoven fabric or a plastic sheet is adhered to the surface of an expanded polystyrene resin formed product is adopted. However, in this method, a large number of steps is required, leading to a steep rise in processing cost.